1. Field of the Invention
The present invention relates to an electrode for a non-aqueous electrolyte secondary battery that can be easily produced and has excellent load characteristics and charge-discharge cycle characteristics, a non-aqueous electrolyte secondary battery using the electrode, and a method for manufacturing the non-aqueous electrolyte secondary battery.
2. Description of Related Art
A non-aqueous electrolyte secondary battery such as a lithium ion secondary battery is characterized by a high energy density and thus has been widely used as a power source for portable equipment such as a portable telephone and a notebook personal computer. It is increasingly important to improve various battery characteristics and safety as the performance of the portable equipment becomes higher.
In the current lithium ion secondary battery, e.g., a polyolefin-based porous film with a thickness of about 10 to 30 μm is used as a separator that is interposed between a positive electrode and a negative electrode. However, when this polyolefin-based porous film is produced, complicated processes such as biaxial orientation and the extraction of a pore-forming agent are required to make fine and uniform pores. Under the present circumstances, therefore, the cost of production is high, and the separator is expensive.
Polyethylene having a melting point of about 120 to 140° C. is used as a material of the separator to ensure a so-called shutdown effect. During the shutdown, the resin constituting the separator is melted at a temperature not more than the abnormal heat generation temperature of the battery, and the pores of the separator are closed. This increases the internal resistance of the battery, thereby improving the safety of the battery when a short circuit or the like occurs. However, e.g., if the temperature of the battery is further raised after the shutdown, the molten polyethylene is likely to flow, and the separator can be broken, which is so-called meltdown. In such a case, the positive electrode and the negative electrode are brought into direct contact, and the temperature of the battery becomes even higher, so that the inside of the battery may be in a dangerous state.
In order to prevent a short circuit due to the meltdown, a method has been proposed that uses a heat-resistant separator in which ceramic particles are applied to a polyethylene microporous film, or a separator composed of a heat-resistant resin. For example, JP 2010-170770 A discloses a non-aqueous electrolyte secondary battery including a positive electrode, a negative electrode, and a separating material that is formed on the surface of the positive electrode or the negative electrode, has a cross-linked structure, and functions as a separator. The technology disclosed in JP 2010-170770 A can improve the safety of the non-aqueous electrolyte secondary battery at a high temperature.
Even in the case of the non-aqueous electrolyte secondary battery with improved safety and reliability (particularly safety and reliability at a high temperature), as described above, it is expected that the load characteristics and the charge-discharge cycle characteristics will need to be further improved, e.g., as the performance of the applicable equipment becomes higher in the future. Moreover, the productivity will also need to be improved. In this respect, there is yet room for improvement in the technology of JP 2010-170770 A.
With the foregoing in mind, the present invention provides an electrode for a non-aqueous electrolyte secondary battery with excellent load characteristics and charge-discharge cycle characteristics, a non-aqueous electrolyte secondary battery using the electrode, and a method for manufacturing the non-aqueous electrolyte secondary battery.